More than five hundred million golf balls are produced each year, of which, a significant percentage have some type of decorative logo printed on their outer surface. For example, many logos advertise or identify a particular corporate entity, golf course, country club, or resort.
Currently, two different approaches are commonly used to add decorative logos to the dimpled surface of golf balls. One approach is to first create a decal of the logo, apply the decal to the spherical, dimpled golf ball surface, and then spray the golf ball cover with a clear finish. This decal process is limited in several different ways. First, decals are generally purchased by the golf ball manufacturer from a vendor or secondary printing source. Defective or off-color decals must be returned to the vendor, potentially causing delays in providing customers with orders within a competitive time frame. Furthermore, decals are expensive and the material and labor costs for adding decals to the dimpled surface of a golf ball averages four to seven times what it would cost to pad-print logos onto a golf ball. Additionally, the variety of colors and/or shading of those colors can be limited by the manufacturing and printing process of decals. Decals are typically made using a silk screening process which, by its nature, limits the number of colors and inhibits the use of shading.
The second approach to adding a logo to the dimpled surface of a golf ball is pad printing. Pad printing is an indirect intaglio process. Depressions representing the logo of choice are created on a flat surface called "the plate" or pad printing cliche. There are two types of plates--variable depth relief photopolymer plates and fixed depth relief plates. The depressions for logos having multiple colors require multiple plates that are dedicated to each individual color of the image to be printed. A plate for each color in the image is etched, by way of a photoactive polymer and a film positive, by UV light. In the case of variable depth relief photopolymer plates, after an initial exposure period, the logo and plate are completely covered with a screen film and exposed to UV light again ("screening"); this step is not necessary for fixed depth relief plates. Screening is a process that places many small "dots," in the shape of truncated cones, into the surface of the etched image itself.
The screen film can have frames of about 50 to 1,000 lines per inch or, more preferably, from about 100 to 300 lines per inch. For example, if the screen film has 80 lines/cm, there will be 64 small circular surfaces per mm.sup.2, each with a diameter of 0.02 to 0.03 mm. This also explains why only high-quality, fine grained material can be used for making the plates. The quality and sharpness of the printed image are still maintained, as the screen spots show only very slightly at the edges.
The pad printing process begins by spreading ink across the surface of the plate with a spatula. Excess ink is then scraped back into an ink reservoir using a "doctor blade" which leaves ink only in the depressions on the plate. As the plate is exposed to air, thinner evaporates from the remaining ink in the depressions causing the ink surface to become tacky. A smooth, resilient, stamp block of silicone rubber is used to lift ink from the plate and transfer it to the golf ball surface. The stamp block is termed a "pad" and it is this term that has lent its name to the printing process. As the pad is lowered over the depressions in the surface of the plate, the tacky ink sticks to the pad. As the pad lifts, it takes with it not only the tacky, adhering film of ink, but also some excess fluid ink underneath. This film of ink is carried on the pad to the target area on the dimpled golf ball surface. The time that elapses during this transfer process allows thinner to evaporate from the exposed surface of the ink on the silicone pad, and the ink surface facing away from the pad becomes tacky. As the pad is applied to the golf ball surface, the tacky film of ink adheres to the ball surface and separates from the pad as it is lifted from the surface.
The pad printing process of adding logos to golf balls, which is used as an alternative to the decal method, requires less time and is less expensive than the decal method. Pad printing is not without problems, though. Printing certain types of images sometimes results in non-uniform color, a print quality problem known to those skilled in the art as "shading." Additionally, some images exhibit non-uniform screening. This problem typically results from variations in depth of etch between the plurality of truncated cones within each etched area on the plates. Further, certain colors are difficult to color-match, especially with the truncated cones present in the etch which further "dilute" the vibrancy of the color. It is clear that most of the current problems arise from the etching of the plates and ink transfer therefrom.
There are two basic types of photopolymer plate materials available--alcohol wash and water wash plates. Water wash plates are the preferred plate because of obvious environmental and safety issues. Within these two categories there are two styles of plates--fixed depth and variable depth plates. Fixed depth plates are just that--the depth of etch cannot be varied. Along the same lines, variable depth plates allow the depth of etch to be optimized for a particular application. The standard depth of etch for fixed depth steel plates is typically 0.001 in (25.4 .mu.m). Fixed depth plastic plates, of which there are precious few (there are only two commercially available fixed depth plates, the T-30 alcohol wash plate and the WT-30 water wash plate, both from BASF), are manufactured to the same standard, having a relief layer of 0.001 in. The more common variable depth plastic plates, such as the WSA-52, commercially available from BASF, are manufactured with much thicker photosensitive relief layers that allow a large variation in depth of etch to be obtained. While a 0.001-in depth of etch is the standard for most pad printing applications, it is too deep to be used successfully with the present invention. Additionally, one of ordinary skill in the art is aware that with the water wash, a fixed depth plate lacks the hardness to be used successfully with many current pad printing methods, such as a scaled ink CLIP system.
The processing procedures, as specified by all plate suppliers/manufacturers, for variable relief plates call for the use of a screen tint (creating the truncated cones discussed above) to control the depth of etch and, therefore, the amount of ink picked up by the pad and transferred to the product, in this case a golf ball. A secondary and important benefit of the screen exposure step is to create a support structure in the etch to prevent the doctor blade from scooping ink as it passes over larger (open) areas of the graphic design. As discussed above, the screen exposure step results in a uniform pattern of truncated cones formed in the etch that, when done properly, results in a similar capacity for ink transfer as a standard open etch steel plate. The advantages are thus numerous: the doctor blade is supported by the small truncated cones, preventing it from dropping into the open areas and remove too much ink in a non-uniform manner; the truncated cones created by the screening step hold back the ink evenly; additionally, the pad is further supported by the small truncated cones and can not squeeze out the ink as it touches the surface. All of these advantages result in homogeneous Ink pick resulting in a quality imprint.
Therefore, one of ordinary skill in the art would not normally attempt to process a variable depth plastic plate without the screen. It is considered very difficult to control the depth of etch (and subsequently the ink transfer) without the screen step. One or ordinary skill in the art, in an attempt to control this, would normally or logically attempt to qualify a commercially available fixed depth plastic plate rather than attempt the unorthodox steps proposed by the present invention.
U.S. Pat. No. 5,778,793 discloses a method of adding a multiple colored logo or gradient shaded logo to the dimpled surface of a golf ball. A method of adding a gradient shaded or multicolored logo to a golf ball is also disclosed, in which a pattern or logo comprising more than one region is formed on a pad printing cliche. Each region comprises many depressions of substantially uniform depth and size. The depressions are also randomized such that there are at least two regions in which the distance between the depressions making up the region varies, creating a gradient shading effect. The number of colors is typically limited to four and each color may only be printed individually, and only opaque inks can be employed to attain the logo colors. If more than 4 colors are desired, correct alignment of the printing machinery, called registration, to add the extra set of colors is difficult. Additionally, use of a screen is required, along with many manufacturing steps, changes in the process if additional colors are to be used, all of which add to the total cost of printing a logo on golf balls.